Pachynus denticulatum Lowry, 1984

Lowry, J. K. & Stoddart, H. E., 2012, The Pachynidae fam. nov. (Crustacea: Amphipoda: Lysianassoidea) 3246, Zootaxa 3246 (1), pp. 1-69 : 40-42

Pachynus denticulatum Lowry, 1984

( Figs 27 , 28a, b )

Pachynus denticulatum Lowry, 1984: 84 , figs 25–27. ― Barnard & Karaman, 1991: 510. ― Springthorpe & Lowry, 1994: 14. Pachynus denticulatus . ― Lowry & Stoddart, 2003: 169.

Material examined. One ovigerous female, 2.8 mm, AM P.46676, Horseshoe Reef, outer Barrier Reef , off Bootless Bay , Papua New Guinea, approx. 9°36'S 147°17'E, 30 m, steep sand and shell slope at base of front face, 28 October 1980, S. Arnam, stn PNG-19. – 1 male, AM P.46677, same locality, sand, 44 m, 9 November 1980, J.K. Lowry & S. Arnam, stn PNG-60. – 1 specimen, AM P.46613, off Cape Banks, New South Wales, Australia, 34°S 151°16'E, 25–30 m, sand, November 1990, The Ecology Lab. – 2 specimens, AM P.46614, same data, 45–50 m. – 3 specimens, AM P.46616, south-east of Bate Bay , New South Wales, Australia, 34°05.9'S 151°12'E, 45–50 m, sand, 24 January 1990, The Ecology Lab, stn Cobblers T1 S2 R2 . – 1 specimen, AM P.46615, same data, July 1990, stn Cobblers S 2 R2 . – 1 specimen, AM P.46618, south-east of Bate Bay , New South Wales, Australia, 34°06.8'S 151°10'E, 45–50 m, sand, July 1990, The Ecology Lab, stn T2 S3 R2 . – 1 specimen, AM P.46617, same data, January 1991, stn T4-331 . – 41 specimens in 9 lots, AM P.46602 to P46610, off Bass Point, New South Wales, Australia, 34°36'S 150°54'E, 35–70 m, sand, November 1990 to January 1991, The Ecology Lab. – 6 specimens, AM P.46397, off Wattamolla, New South Wales, Australia, 34°44'S 150° 39'E, 45–50 m, sand, January 1990, The Ecology Lab, stn S1 R3 . – 3 specimens, AM P.46612, same data, stn S3. – 1 specimen, AM P.46557, same data, 35–40 m, stn S2 R2 . – 6 specimens, AM P.46611, same data, stn S3. – 1 specimen, AM P.46675, off Providential Head, New South Wales, Australia, 34°44'S 150° 39'E, 25–30 m, baited trap set overnight, 15 January 1991, S.J. Keable, A. Parker & J.K. Lowry, MV Krista, stn PIO-109. – 3 specimens (including ovigerous female), AM P.68501, east of Lakes Entrance , Victoria, Australia, 37°55.6’S 148°15.1’E, 41 m, benthic sled, 25 August 1994, P.B. Berents, FRV Southern Surveyor , stn 05/94/41. – 7 specimens, MV J22338 , 10.5 km east-south-east of eastern edge of Lake Tyers , Victoria, Australia, 37°54.07'S 148°12.09'E, 42 m, sand and shell, Smith-McIntyre grab, 25 September 1990, Marine Science Laboratories, stn MSL-EG 32. – 2 specimens, MV J22339 , 8.6 km west-south-west of Cape Conran, Victoria, Australia, 37°51.19'S 148°38.53'E, 51 m, mud and shell, Smith-McIntyre grab, 28 September 1990, Marine Science Laboratories, stn MSL-EG 56. – 1 specimen, MV J62410 , 85 km north-east of North Point , Flinders Island , eastern Bass Strait , Australia, 39°02.4'S 148°30.6'E, 120 m, muddy sand, 15 November 1981, R. Wilson, RV Tangaroa, stn BSS 169. – 1 specimen, MV J2501 , 42 km south-west of Babel Island , Tasmania, eastern Bass Strait , Australia, 40°14.4'S 148°40.0'E, 60 m, muddy sand, Smith-McIntyre grab, 14 November 1981, R. Wilson, RV Tangaroa, stn BSS-165G. – 4 specimens, MV J62422 , 5 km north of North Point , Tasmania, central Bass Strait , Australia, 40°40.3'S 145°15'E, 33 m, medium shell, epibenthic sled, 4 November 1980, M. Gomon & G.C.B. Poore, FRV Sarda , stn BSS 115S. – 1 specimen, MV J62412 , same data, Smith-McIntyre grab, stn BSS 115G .

Diagnostic description. Head lateral cephalic lobe small, subacute; ventral margin curved. Antenna 1 peduncular article 1 without posterodistal spine; accessory flagellum absent; flagellum with weak 1-field callynophore in female, strong 1-field callynophore in male. Mandible lacinia mobilis a simple robust seta; lamina dentata absent; accessory setal row present, not on raised setose ridge; molar absent; palp attached midway; palp article 2 slender, longer than article 3; article 3 with subparallel margins. Maxilla 1 outer plate with 8 setal-teeth in 5/3 arrangement, setal-teeth smooth; palp well developed, 2-articulate, with apical robust setae. Maxilliped inner plate small; outer plate small; palp 4-articulate, article 4 large. Gnathopod 1 chelate; ischium smaller than propodus, not swollen posteroproximally; carpus extremely compressed; propodus length about 1.6 × breadth, posterior margin well developed, with produced corner, corner of palm with complex robust seta; dactylus reaching to corner of palm. Gnathopod 2 propodus, length more than 2 × breadth, palm minute, transverse. Pereonite 4 without dorsal spines. Pereonite 5 without dorsal spines. Pereopod 5 merus with posteroproximal shoulder. Pereopod 6 basis with posteroventral lobe produced beyond ischium; merus broader than long, with posteroproximal shoulder. Pereopod 7 basis subquadrate, about 1.5 × as long as wide with posterior margin weakly dentate. Epimeron 3 posterior margin without projections, posteroventral corner acutely produced. Uropod 3 biramous, inner ramus just reaching base of article 2 of outer ramus. Telson longer than broad, entire.

Remarks. Pachynus denticulatum and P. pugilator both have the epimeron 3 posteroventral corner acutely produced. They differ in the accessory flagellum (present in P. pugilator , absent in P. denticulatum ); in mandibular palp article 2 (subequal to article 3 in P. pugilator , longer in P. denticulatum ); and in the shape of the pereopod 5 basis (subovate in P. pugilator , subquadrate in P. denticulatum ). The shape of the epimeron 3 posteroventral corner varies slightly, as shown in fig. 28.

Distribution. Southern Papua New Guinea and south-eastern Australia, western South Pacific Ocean; 25–120 m depth.

Figures

FIGURE 27. Pachynus denticulatum Lowry, 1984. Female, 4.0 mm, MV J62422, Bass Strait, Tasmania, Australia. Scales represent 0.1 mm.

FIGURE 28. Posteroventral corner of epimeron 3. a: Pachynus denticulatum Lowry, 1984, holotype, 3.4 mm, AM P.24232, off Malabar, New South Wales, Australia; b: P. denticulatum, female, 2.8 mm, AM P.46676, off Horseshoe, Reef, Bootless Bay, Papua New Guinea; c: P. pugilator Lowry, 1984, female, 3.6 mm, MV J62416, Crib Point, Western Port, Victoria, Australia.